1. Field of the Invention
The present invention relates to a positive resist composition and a patterning process using the same.
2. Description of the Related Art
In an ArF immersion lithography, a proposal is made to impregnate water between a projector lens and a wafer. A refractive index of water at 193 nm is 1.44, and therefore a pattern formation is possible even if a lens with a numerical aperture (NA) of 1.0 or more is used, and moreover, theoretically NA may be increased to near 1.35. A miniaturization to a level of 45 nm or lower becomes possible by combination of a lens having NA of 1.2 or more and a super-resolution technology (Proc. SPIE Vol. 5040 p 724).
In the immersion lithography, various problems have been pointed out due to presence of water on a resist film. Namely, the problems include a pattern profile change and contamination of a projection lens of an exposure apparatus, due to leaching of a photoacid generator in the resist composition; an acid generated by photoirradiation; an amine compound added to the resist film as a quencher; and the like, to water which is in contact with the resist film.
In order to avoid these problems, a measure has been taken to form a top coat on a resist film to suppress the leaching. However, although the leaching could be suppressed by the top coat, there appeared problems of deterioration in pattern profile and resolution. As to the pattern profile, there was a problem of causing a round head, namely, a top loss.
On top of that, as the requirement of higher resolution increases, improvement in various lithography performances is wanted. In particular, in order to improve a process margin and so on during patterning, improvement of characteristics in Depth of Focus (DOF) is wanted.